Some old workhorses never die, and one of them is email. According to Retention Science, a marketing data firm, email "generated the highest ROI for eCommerce in 2014." Not only that, email "consistently outperforms other channels in engagement and conversion."
You know those Millennials marketers are always trying to engage and influence? Retention Science reports that 47 percent of them prefer to communicate with brands via email, while only 6 percent choose social media.
In terms of email effectiveness, Retention Science found that "percent off" vs. "dollar off" deal emails generate more clicks and more conversions. As for those very important email subject lines, 6 to 10 words result in optimal open rates, and any punctuation in a subject line increases open rates -- but question marks are especially effective.
Retention Science based its observations on a massive survey of 1 billion emails from a cross-section of retailers that resulted in 60 million orders of the last two years.